Who is Responsible for this Cat's Death and What Do I Do?

I really need some helpful advice. I am so upset over this I just can't think straight perhaps you can help me.

I run a homeless cat shelter. Recently, I had about two tons (literally) of dog food donated to me. I called my vets office and found plenty of people to distribute it to.

Three people from my vet's office came last Friday to pick up the dog food. I had a cat that I was a bit worried about. He would not gain weight and had diarrhea all the time. I was afraid he had some kind of disease or something. He was rescued from a dumpster and was obviously a very inbred cat. When the cat left here, he was just the way he had always been. He was fine except for his diarrhea. He ate just fine, was active, etc.

The vet's office called me the next day and told me that he just needed to be on a no fat diet because he could not digest fat. He also had a tapeworm (from eating a live flea) and was given medication for that. I told them I could not pick the cat up until this morning, as I didn't have transportation.

I went this morning to pick up the cat. I had to drop my husband off at work so I was in town around 7 a.m. I was told the cat was at the secretary's (of the vet) home. I went to her home to pick up Crier. When I got there Crier was in a cat carrier on her porch. It has been cold here all weekend. He had been in that carrier on the porch all weekend. He was wet and filthy! He was so weak. When he heard my voice he shakily got himself up and came out to me. I asked her what happened to him. She said, I don't know. He just got this way yesterday. My phone has been messed up for days and she couldn't call me.

I brought Crier home, gave him a warm bath, and tried to get some kitten baby formula down him, as he was not strong enough to eat. I put him wrapped dry and on a heating pad. I laid down with him for a couple of hours talking to him and he responded to me. My heart broke as he cried in such a weak sad voice. He died two hours later.

I am so angry. He was fine when he left here Friday. I feel like the secretary caused his death by putting him in that carrier and leaving him cold, wet, and filthy on her porch. I felt comfortable with Crier being at her house because she has dogs, cats, and two chinchillas. They are all healthy and happy animals.

She was outside waiting for her ride to work when I got there this morning, so she obviously was just going to leave Crier there in his own wet filth while she went to work at the vet's office!

What do I do? She and I had become friends but I feel so betrayed. That little cat suffered all weekend probably thinking I abandoned him.

My vet has been the most compassionate and caring man. He lets me run up a bill because he knows I will pay it when I can. I trust him explicitly. But, now, I am afraid. I don't know if I feel safe with that woman there. Perhaps I am overreacting. I just don't know.